This invention concerns bioactive sol-gel derived silica fibers, methods for their preparation, an implantable device comprising said fibers and the use of said device for tissue guiding or bone repair.
The publications and other materials used herein to illuminate the background of the invention, and in particular, cases to provide additional details respecting the practice, are incorporated by reference.
The sol-gel method has widely been used as an alternative method to prepare a great variety of applications including monoliths, powders, coatings and fibers. A growing field of interest has been bioceramics that can be used as implants, fillers, or drug delivery devices.
The rheological properties of the silica sols and the processing of the sol-gel derived silica fibers are well known.1-9 The most common property of the sols in the fiber spinning is a low water-to-TEOS molar ratio (about 2) (TEOS=tetraethylorthosilicate or tetraethoxysilane). The low water-to-TEOS ratio indicates a formation of linear silica polymers, which is an important factor for the spinnable sols. Various sol-gel derived fibers (containing Ti, Si, A, Pb, Y, Mg or Al) have also been successfully prepared.5,6,10-13 The most common use for these fibers are the applications for optical and electronic purposes.14-27 
In general, the fibers have been used to improve mechanical properties in different materials. The bulk structure of the sol-gel derived silica fibers can be varied by controlling the degree of branching of silica clusters. The heat treatment of the fibers is another known method for condensing the bulk structure. The mechanical properties become better after heat-treatment at high temperatures. In applications where the fibers are used as drug delivery device in soft tissue, the mechanical properties are of minor importance. If better mechanical properties are needed, it has to be noted that the biodegradation reduces after heat-treatment at high temperatures. In the inventors"" previous article28 the biodegradation of the sol-gel derived silica fibers (which was not heat-treated) was studied. It was found that the biodegradation of the green state fibers can be varied and controlled by adjusting the stage of spinnability (by varying the spinning moment) and the viscosity of the sol. It was found that fibers spun in the early stage of spinnability degrade more slowly in the simulated body fluid (SBF) than fibers spun at a later stage.
Another important property of the biomaterials, bioactivity, has been widely studied also for sol-gel-derived materials. The ability of the materials to form HCA (HCA=bone like calcium phosphate) may lead to osteoconduction and further to bone bonding in in vivo conditions.29,30 
The formation of the HCA layer can be simulated in an in vitro environment by using simulated body fluid. The SBF solution contains inorganic ions in concentrations corresponding to the human blood plasma.31 The formed HCA has several characteristics similar to the apatite in the bone tissue and it is thought to be formed by an inorganic chemical reaction in vitro similar to that occurring in the bone tissue. This in vitro bioactivity test is generally accepted to give an indication of the in viva bioactivity.32 
Bioactive sol-gel-derived silica fibers are not mentioned in prior art. Such bioactive silica fibers would provide alternatives for the design of novel products, for example implantable devices to be used in tissue guiding or bone repairs.
The aim of this invention is to provide a bioactive sol-gel derived silica fiber. The aim is particularly to provide a sol-gel derived silica fiber, the solubility and bioactivity of which can be varied within a wide range and where the solubility and bioactivity can be varied to some extent independently of each other.
Another object is to provide a method for the preparation of a bioactive sol-gel derived silica fiber of the aforementioned kind.
Still one object is to achieve an implantable device based on the aforementioned fiber, optionally loaded with a biologically active agent, wherein said device preferably is in the form of a woven or non-woven mat, a knitted fabric or a braided cord, particularly suitable for use as tissue guiding or bone repair.
Thus, according to one aspect, this invention concerns a bioactive sol-gel derived silica fiber spun from a sol at a starting point of the spinning process corresponding to a sol viscosity of at least 2000 cP, after which said fiber has been subjected to i) heat treatment or ii) aging.
According to another aspect, this invention concerns a method for the preparation of a bioactive sol-gel derived silica fiber, said method comprising spinning the fiber from a silica sol wherein the starting point of the spinning process corresponds to a sol viscosity of at least 2000 cP, followed by i) heat treating or ii) aging of the fiber.
According to a further aspect, this invention concerns an implantable device comprising a fiber according to this invention.
Furthermore, this invention concerns the use of the implantable device according to this invention for tissue guiding or bone repair.